(Updated 2026) Fungal nails - also known as onychomycosis (OM)  - are a very common condition that podiatrists see every day. While fungal toenails are not usually serious, many people are bothered by the thickening, discolouration and crumbling  they can cause. Some people also experience discomfort, pressure in shoes or embarrassment about the appearance of their nails. In this post, I’ll explain: What causes fungal toenails How fungal nail infections spread How to prevent